The present invention relates generally to antennas, and in particular, to an improved antenna for a wristworn device having signal transmitting and/or receiving capabilities. In exemplary embodiments, the wristworn device is a timepiece such as a wristwatch, but, as will become quite clear below, a timepiece or wristwatch is only by way of example and not limitation. In particular, the invention is primarily directed to improved signal transmission and reception within a metal casing, such as a casing for a timepiece.
The prior art is full of examples of antennas associated with wristworn devices, such as wristwatches. As would be well known to those skilled in the art, loop antennas are particularly advantageous due to their size and directivity, as it is well known that a loop antenna is desirable since it has a geometry that essentially “pulls in” signals from 360 degrees (i.e. from all different azimuths and orientations). For example, U.S. Pat. Nos. 5,072,231; 6,104,354; 6,028,555 and 6,154,177 are but just a few examples of devices incorporating loop antennas for signal reception and transmission. While these arrangements may have been satisfactory for their intended uses, they all are perceived to be deficient in various respects.
The use of loop antennas for signal reception and transmission has been found to be particularly desirable in devices, such as timepieces. However, use of a loop antenna in a metal case, such as a watch casing, has been found to have drawbacks and to be less than optimal, typically because of the poor performance due to the shielding of the antenna by the metal case itself. Additionally, electro-static discharge (ESD) is also a known problem when using a metal casing.
Introducing a slot in the case to improve signal reception or transmission is known. For example, the inventor is aware of at least one device that had therein an RFID transmitter/receiver, which incorporated a slotted casing. However, this known example utilizes a coil antenna with a ferrite core, which doesn't provide a desirable distance communication range. Moreover, the use of coil antennas in such devices are limited to short range (e.g. 1–2 feet) communications, which are less than desirable in the communications contemplated by the present invention.
With all of the known obstacles related to shielding and performance of a loop antennas in a metal casing, it is believed that the prior art designs have been less than effective in incorporating a loop antenna into a device having a metal casing. Even more remote is the idea of using the metal casing itself as the loop antenna. However, as discussed below, the present inventor has recognized that when a slotted casing is used as the actual antenna or when the loop is placed underneath and the case is used a “re-radiator,” signal reception/transmission performance is significantly improved.